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antenna interference

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Mon Oct 23, 2006 10:44 am Post subject: antenna interference

10/23/2006



Hello Bob Nuckolls and other antenna experts,



 Some time ago a fellow builder installed an Advanced Aircraft Electronics 

comm antenna in

the vertical stab of his composite (fiberglass) airplane.  The antenna is a 

straight one piece dipole with balun in  center.



The reception was tested with a radio and found to be excellent.  In 

attaching the rudder, a full length aluminum piano style hinge was 

installed. This is one of the builder's modifications to the original plans 

that called for separate short segments of aluminum piano type hinge for the 

rudder.



When testing the reception again with the same transmitter the reception was 

practically nonexistent.



The builder would like to retain use of the antenna and come up with a 

(nearly continuous) hinge solution that will permit adequate transmission 

and reception. Various solutions have been proposed:



1) Use a continuous piano type hinge made out of plastic. (Guden makes 

them).



2) Use a continuous piano type hinge made out of carbon fiber.



http://www.carbinge.com/index.html



3) Use a basically continuous full length piano type hinge made out of 

carbon fiber, but cut it a number of times during its length into shorter 

than full length segments.



4) Use a basically continuous full length piano type hinge made out of 

aluminum, but cut it a number of times during its length into shorter than 

full length segments.



5) Abandon the continuous hinge concept and install separate short segments 

of metal hinge as the plans call for.



We would appreciate your inputs and advice. Thanks.



OC

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nuckollsr(at)cox.net
Guest

Posted: Mon Oct 23, 2006 11:25 am Post subject: antenna interference

At 02:41 PM 10/23/2006 -0400, you wrote:



 	  Quote: 	
		  



10/23/2006



Hello Bob Nuckolls and other antenna experts,



Some time ago a fellow builder installed an Advanced Aircraft Electronics 

comm antenna in

the vertical stab of his composite (fiberglass) airplane.  The antenna is 

a straight one piece dipole with balun in  center.



The reception was tested with a radio and found to be excellent.  In 

attaching the rudder, a full length aluminum piano style hinge was 

installed. This is one of the builder's modifications to the original 

plans that called for separate short segments of aluminum piano type hinge 

for the rudder.



When testing the reception again with the same transmitter the reception 

was practically nonexistent.



The builder would like to retain use of the antenna and come up with a 

(nearly continuous) hinge solution that will permit adequate transmission 

and reception. Various solutions have been proposed:


	


    Hmmmm . . . "adequate" is the operative word here. Without

    laboratory data on the effects of current configuration and

    any hypothesized solutions will be hip-shots . . .

 	  Quote: 	
		  1) Use a continuous piano type hinge made out of plastic. (Guden makes them).


	


    As a structural part of the airplane?

 	  Quote: 	
		  2) Use a continuous piano type hinge made out of carbon fiber.



http://www.carbinge.com/index.html


	


   I presume the rest of the structure is carbon fiber also. This

   solution is relatively attractive but know that carbon fiber

   while not an excellent conductor . . . it's also very unfriendly

   to RF propagation. At least the hinge material would not be any

   worse than structural components around it

 	  Quote: 	
		  3) Use a basically continuous full length piano type hinge made out of 

carbon fiber, but cut it a number of times during its length into shorter 

than full length segments.


	


   Cutting a carbon fiber hinge would produce minimal

   benefit once the shift from aluminum to carbon fiber is made.

 	  Quote: 	
		  4) Use a basically continuous full length piano type hinge made out of 

aluminum, but cut it a number of times during its length into shorter than 

full length segments.


	


   This works . . . when driving past AM station towers

   (tower itself is the antenna) one observes that guy wires

   are broken up into short segments by strain insulators.

   The rule of thumb is that a parasitic conductor's length

   should not exceed 1/10th wavelength at frequency of interest.

   In the case of VHF Comm, about .2 meters or 8 inches in length

   or shorter.

 	  Quote: 	
		  5) Abandon the continuous hinge concept and install separate short 

segments of metal hinge as the plans call for.


	


   That works too . . . but probably no better than segmented

   hinges of other materials.



   Bob . . .

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douglist(at)macnauchtan.c
Guest

Posted: Mon Oct 23, 2006 12:49 pm Post subject: antenna interference

At 14:41 -0400 10/23/06, <bakerocb(at)cox.net> wrote:

 	  Quote: 	
		  4) Use a basically continuous full length piano type hinge made out of aluminum, but cut it a number of times during its length into shorter than full length segments.


	


It might be sufficient to cut it once only a few inches away from the center.



It might also be enough to cut just the rod into two pieces with an insulator between them



You might also try bonding both sides of the hinge to airframe ground. Well. . . that doesn't mean connecting it to the fiberglass. The idea is to move the resonance to longer wavelengths by making the hinge electrically longer as opposed to cutting it to make it shorter.



And the # 10 thought. . . . Remove the dipole antenna and put a BNC connector on the hinge.



-- 

--> If  it's not  on  fire  it's  a  software  problem. <--

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ceengland(at)bellsouth.ne
Guest

Posted: Mon Oct 23, 2006 5:20 pm Post subject: antenna interference

Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 At 02:41 PM 10/23/2006 -0400, you wrote:



> 

>

> 10/23/2006

>

> Hello Bob Nuckolls and other antenna experts,

>

> Some time ago a fellow builder installed an Advanced Aircraft 

> Electronics comm antenna in

> the vertical stab of his composite (fiberglass) airplane.  The 

> antenna is a straight one piece dipole with balun in  center.

>

> The reception was tested with a radio and found to be excellent.  In 

> attaching the rudder, a full length aluminum piano style hinge was 

> installed. This is one of the builder's modifications to the original 

> plans that called for separate short segments of aluminum piano type 

> hinge for the rudder.

>

> When testing the reception again with the same transmitter the 

> reception was practically nonexistent.

>

> The builder would like to retain use of the antenna and come up with 

> a (nearly continuous) hinge solution that will permit adequate 

> transmission and reception. Various solutions have been proposed:

    Hmmmm . . . "adequate" is the operative word here. Without

    laboratory data on the effects of current configuration and

    any hypothesized solutions will be hip-shots . . .

> 1) Use a continuous piano type hinge made out of plastic. (Guden 

> makes them).

    As a structural part of the airplane?

> 2) Use a continuous piano type hinge made out of carbon fiber.

>

> http://www.carbinge.com/index.html

   I presume the rest of the structure is carbon fiber also. This

   solution is relatively attractive but know that carbon fiber

   while not an excellent conductor . . . it's also very unfriendly

   to RF propagation. At least the hinge material would not be any

   worse than structural components around it

> 3) Use a basically continuous full length piano type hinge made out 

> of carbon fiber, but cut it a number of times during its length into 

> shorter than full length segments.

   Cutting a carbon fiber hinge would produce minimal

   benefit once the shift from aluminum to carbon fiber is made.

> 4) Use a basically continuous full length piano type hinge made out 

> of aluminum, but cut it a number of times during its length into 

> shorter than full length segments.

   This works . . . when driving past AM station towers

   (tower itself is the antenna) one observes that guy wires

   are broken up into short segments by strain insulators.

   The rule of thumb is that a parasitic conductor's length

   should not exceed 1/10th wavelength at frequency of interest.

   In the case of VHF Comm, about .2 meters or 8 inches in length

   or shorter.

> 5) Abandon the continuous hinge concept and install separate short 

> segments of metal hinge as the plans call for.

   That works too . . . but probably no better than segmented

   hinges of other materials.



   Bob . . . 


	




Or, he could break the AL hinge once in the middle & use it as the dipole.



(I haven't even stayed in a Holiday Inn recently; please don't take this 

seriously.)

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nuckollsr(at)cox.net
Guest

Posted: Tue Oct 24, 2006 5:27 am Post subject: antenna interference

 	  Quote: 	
		  

Or, he could break the AL hinge once in the middle & use it as the dipole.



(I haven't even stayed in a Holiday Inn recently; please don't take this 

seriously.)


	


   Actually, I considered that too . . . and it's quite doable. However,

   it takes some time and understanding to do the system integration.

   We have HF antennas on the bizjets that depend on certain structural

   characteristics to be in place for optimum performance. Because

   the HF system was an accessory added some 30 years after the

   airplane was designed, there's no symbiotic relationship possible

   between structure and antenna. The structure becomes as much an

   "antenna" as the intended radiator wreaking havoc on numerous

   on-board systems.



   In this case, the proposed hinge-dipole is probably doable

   within limits for structural integrity needed for keeping the

   rudder attached!



   Can the hinge be 40" or longer?



   Bob  . . .

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